1. Field of the Invention
This invention relates to a heating unit of a carbon fiber-mixed sheet which sheet is produced by the mixed sheet-making of a carbon fiber along with a plant pulp, especially with a pulp containing a bast fiber.
2. Description of the Prior Art
Petroleum and gas-burners and electric heating appliances have gained a wide application as heating units. Planar heaters using electric heating such as panel heaters have also been used as appliances for local heating. Among such planar heaters using electric heating, heaters for radiating far infrared rays have drawn an increasing attention in recent years because the far infrared rays have high penetration force through clothes, etc., and have high heating efficiency.
Metallic heating materials having a high electric resistivity such as a nichrome wire have been mainly used as a heat source of the heaters for radiating the far infrared rays. Carbon powder, ceramics, etc., are disposed on the surface, and when heated, they irradiate the far infrared rays.
In the planar heating units for radiating the far infrared rays, on the other hand, they preferably provide a temperature distribution, which is as uniform as possible, throughout the entire surface thereof. In the heating units using the nichrome wire as the heat source of the planar heating units, therefore, the nichrome wires must be divided into zones as finely as possible and a temperature regulation member such as a thermostat must be disposed for each zone.
To cope with this problem, the applicant of the present device has proposed a planar heating unit using a carbon fiber-mixed sheet. As shown FIG. 6, this planar heating unit 010 is produced by mixing a bast fiber 01 for Japanese paper such as Broussonetia Kazinoki Sieb, Musa Textilio and Edgeworthia Papyrifera with a carbon fiber 02 and by subjecting the mixture to sheet-making. About 5 to about 15% of a PAN-type carbon fiber having a filament diameter of 6.8 xcexcm and a resistivity of about 20 xcexcxcexa9 is mixed as the carbon fiber. When the sheet-making is carried out by mixing such a bast fiber, a viscous solution extracted from the roots of Hibiscus manihot L. being used as mucilage of Japanese paper is blended.
Electric poles 06, 07 are disposed along side edges 04, 05 of the major sides of a rectangular carbon fiber planar heating unit 010 in the planar heating unit so formed and shown in FIG. 7. for example, and lead wires 08 are connected to terminals provided for the electric poles. When an A.C. voltage of 100 V is applied between both electric poles of the planar heating unit, for example, no critical danger occurs to the human body even when one directly touches the planar heating unit. To produce a practical electric product, however, a synthetic resin sheet 09 is laminated or a suitable synthetic resin thin sheet is bonded to the both surfaces, inclusive of the heating unit portion and the electric poles, and furthermore an aluminum sheet is laminated, in some cases, as shown in FIG. 8 so as to insure waterproofing, moisture proofing, safety, etc., or to prevent damage of the heating unit.
When power is supplied to the carbon fiber so mixed and sheet-made in the planar heating unit, heating occurs due to its resistance. Since the carbon fiber is finely cut and is electrically connected with one another either directly or with very small gaps by the viscous solution extracted from the root of Hibiscus manihot L, etc., a high resistance action takes place at this portion in accordance with the temperature rise, and uncontrolled heating can be prevented.
As described above, the planar heating unit proposed by the public-known applicant has a difficulty to even the mixed pulp-making of a carbon fiber and a pulp fiber and can not provide automatically a uniform temperature distribution throughout the entire surface of the planar heating unit. Nonetheless, when the planar heating unit in which the carbon fiber is mixed and subjected to sheet-making is used for a long time, the synthetic resin thin plate disposed as a protective cover on the surface of the planar heating unit gradually undergoes discoloration or deterioration, and consequently, service life of the planar heating unit is determined by these defects.
A cause difficult for unifying a blend of a carbon fiber and a pulp fiber results from that at the time of paper-making a refined pulp, the refined pulp is adjusted to a specific concentration, beaten in a refiner as shown in FIG. 9, and blended with 5 to 10 wt. %, preferably about 7%, of a carbon fiber having a fiber cut length of about 6 mm agitated in a stuff chest, and from that the carbon fiber, however, because it has a low density and a low friction coefficient while a high tensile strength and a low breakdown elongation, is not satisfactorily blended with the pulp even agitated in the stuff chest, is distributed unevenly in a sheet making machine. Therefore a carbon fiber in the carbon fiber-mixed sheet prepared may often not be dispersed uniformly.
Accordingly, the present device has an object to provide a heating unit of a carbon fiber-mixed sheet in which carbon fibers are evenly dispersed in the carbon fiber-mixed sheet and a member on which sheet surface does not undergo a degradation such as discoloration and which has a low price.
In order to solve the problem described above, the present device provides a heating unit of a carbon fiber-mixed sheet which sheet has a thickness of 150 xcexcm or less, a basis weight of 50 g/m2 or less, and a degree of beating of 30xcx9c70xc2x0 SR and is obtained by the mixed sheet making of 5xcx9c10 wt. % of a carbon fiber with a length of 5xcx9c10 mm and 95xcx9c90 wt. 5 of a pulp containing a bast fiber and furthermore one part of which is covered with a sizing agent.
Having the construction described above, the carbon fiber-mixed sheet according to the present device can automatically form a uniform temperature distribution throughout the entire surface and does not undergo discoloration or degradation in the course of use from a long time, so that it becomes more economical.